The art of infrared (IR) detection has made great strides in recent years. The first detectors used oil films and other types of continuous retina type detecting elements in which lateral heat conduction erased most of the fine detail before the image could be properly evaluated. To overcome this, and a lack of sensitivity in general, the art turned to discrete solid state detectors. Resolution thus become a function of the size of the detecting element and the magnification of the optics, both of which were severely limited by practical considerations of portability and cost. Now with the advent of insulated gate devices and charge coupled arrays the resolution of these detectors is increasing by orders of magnitude.
The effectiveness of these detectors against hostile targets, particularly in military situations has been phenomenal. Being passive devices they can be operated in almost any situation without alerting the target being detected. Also, the most interesting targets, i.e., tanks, trucks, operating weapons and power generators; naturally provide a great contrast to the surrounding environment.
About the only way to defeat these systems is to provide decoys or sources which radiate infrared equal to that of any specific target. For certain targets this is very difficult. Some targets contain highly concentrated heat sources which produce very high localized temperatures. There are also targets that contain a large number of heat sources with distinctive shapes which form easily recognizeable patterns. As the contrast sensitivity of solid state detectors improves it becomes possible to discern, for example, the number of cylinders in a gasoline engine and other subtle distinctions such as a change in fabrication material or perhaps a particular type of seam. If this capability could be defeated the target might be ignored as a less important target or in some cases even mistaken for a naturally occurring phenomenon such as a sun heated rock.